The traditional copper-clad laminate used for printed circuit mainly utilizes brominated epoxy resin and achieves flame retardant function by bromine. But in recent years, carcinogen such as dioxins, dibenzofurans and others are detected in the combustion products of wastes of electrical and electronic equipment containing halogen such as bromine, chlorine etc. Meanwhile, halogen-containing products may release highly toxic hydrogen halide during combustion process. In addition, two environmental protection directives of the European Union “Directive on the waste electrical and electronic equipment” and “Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment” were officially implemented on Jul. 1, 2006. Due to the non-environmental protection property of the combustion products of the halogen-containing products and the implementation of the two environmental protection directives, the development of halogen-free flame retardant copper-clad laminate has become a hot topic in the related industry field, and each copper-clad laminate manufacturer has launched their own halogen-free flame retardant copper-clad laminate in succession.
In recent years, with the development of high performance, high function and networking of computers and information communication equipment, in order to convey at high speed and treat large capacity information, the operation signal tends to be high frequency, and thus requirements on the materials of circuit board are put forward. The current materials used for printed circuit substrate widely use epoxy resins with excellent adhesion property, however, the epoxy resin circuit substrate generally has a high dielectric constant and a high dielectric loss angle tangent value (dielectric constant is greater than 4, dielectric loss angle tangent value is about 0.02), and the high frequency characteristic thereof is insufficient, thus it cannot adapt to the requirements of signal of high frequency. Therefore, a resin with excellent dielectric property, i.e., a resin with a low dielectric constant and a low dielectric loss angle tangent value, must be developed. For a long time, those skilled in the art have studied thermoset resins of polybutadiene or a copolymer of polybutadiene and styrene having excellent dielectric property.
WO97/38564 utilizes a circuit substrate made from nonpolar tetramer of styrene and butadiene and divinyl benzene with aluminum magnesium silicate filler being added and glass fiber cloth as a reinforcing material. Although the dielectric property thereof is excellent, the heat resistance of the substrate is very poor, the glass transition temperature thereof is only about 100° C., the thermal expansion coefficient thereof is very large, and thus it is difficult to meet the requirement of high temperature (240° C.) of the lead-free manufacturing process in the PCB manufacturing process.
U.S. Pat. No. 5,571,609 utilizes a circuit substrate made by coordinating 1,2-polybutadiene resin or polyisobutadiene having a low molecular weight less than 5000 with a copolymer of butadiene and styrene having a high molecular weight, with the addition of a large amount of silica powder as a filler, and glass fiber cloth as a reinforcing material. Although the dielectric property thereof is excellent, due to the use of components having a high molecular weight in the patent to improve the hand-sticky condition of a prepreg, the processing properties during manufacturing the prepreg become poor; in addition, since the proportion of benzene ring having a rigid structure in the resin molecules of the whole resin system is very low and the cross-linked chains mainly consist of methylene with a very low rigidity, the prepared board has a poor rigidity and the flexural strength thereof is very low.
U.S. Pat. No. 6,569,943 utilizes a circuit substrate made from vinyl-terminated amine modified liquid polybutadiene resin, with the addition of a large amount of monomer (dibromostyrene) having a low molecular weight as a curing agent and a diluent, and impregnated glass fiber cloth. Although the dielectric property thereof is excellent, since the resin system is liquid at room temperature, it cannot be made into a non-hand-sticky prepreg, so it is very difficult to use the conventional prepreg stacking process when pressing moulding the board, making the technical operation difficult.
CN1280337C uses unsaturated double bond terminated polyphenylene oxide resin, and utilizes vinyl monomers (such as dibromostyrene) with a low molecular weight as a curing agent. However, since the boiling point of these low molecular weight monomers is low, these monomers evaporate away during the drying process of making a prepreg by impregnating glass fiber cloth, and thus it is difficult to guarantee the adequate amount of the curing agent. In addition, although this patent mentions that polybutadiene type resins can be used to change the viscosity of the system, but it does not explicitly put forward using polybutadiene type resins having polar groups and using polybutadiene type resins having polar groups to improve peeling strength.
CN101544841B uses a hydrocarbon resin with a molecular weight lower than 11000 and a vinyl content higher than 60% as the main material, and uses allyl modified phenolic resin to improve the sticky property of the prepreg. There is a certain promotion in peeling strength, but the heat resistance of the cured system is low, and the copper-clad laminate has a higher failure risk of delamination during the PCB processing.
A system with hydrocarbon resin as the main material has a low adhesion to metal and a low heat resistance, which brings a greater failure risk to the PCB processing in the downstream of manufacturing copper-clad laminate.